<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        body{
            margin: 0px;
        }
        img {
            border: 0;
        }
        ul{
            padding: 0;
            margin: 0;
            list-style: none;
        }
        .clearfix:after {
            content: ".";
            display: block;
            height: 0;
            clear: both;
            visibility: hidden;
        }
        .wrap{
            width: 980px;
            margin: 0 auto;
        }
        .pg-header{
            background-color: #303a40;
            -webkit-box-shadow: 0 2px 5px rgba(0,0,0,.2);
            -moz-box-shadow: 0 2px 5px rgba(0,0,0,.2);
            box-shadow: 0 2px 5px rgba(0,0,0,.2);
        }
        .pg-header .logo{
            float: left;
            padding:5px 10px 5px 0px;
        }
        .pg-header .logo img{
            vertical-align: middle;
            width: 110px;
            height: 40px;

        }
        .pg-header .nav{
            line-height: 50px;
        }
        .pg-header .nav ul li{
            float: left;
        }
        .pg-header .nav ul li a{
            display: block;
            color: #ccc;
            padding: 0 20px;
            text-decoration: none;
            font-size: 14px;
        }
        .pg-header .nav ul li a:hover{
            color: #fff;
            background-color: #425a66;
        }
        .pg-body{

        }
        .pg-body .catalog{
            position: absolute;
            top:60px;
            width: 200px;
            background-color: #fafafa;
            bottom: 0px;
        }
        .pg-body .catalog.fixed{
            position: fixed;
            top:10px;
        }

        .pg-body .catalog .catalog-item.active{
            color: #fff;
            background-color: #425a66;
        }

        .pg-body .content{
            position: absolute;
            top:60px;
            width: 700px;
            margin-left: 210px;
            background-color: #fafafa;
            overflow: auto;
        }
        .pg-body .content .section{
            height: 500px;
        }
    </style>
</head>
<body>
    <div class="pg-header">
        <div class="wrap clearfix">
            <div class="logo">
                <a href="#">
                    <img src="http://core.pc.lietou-static.com/revs/images/common/logo_7012c4a4.pn">
                </a>
            </div>
            <div class="nav">
                <ul>
                    <li>
                        <a  href="#">首页</a>
                    </li>
                    <li>
                        <a  href="#">功能一</a>
                    </li>
                    <li>
                        <a  href="#">功能二</a>
                    </li>
                </ul>
            </div>

        </div>
    </div>
    <div class="pg-body">
        <div class="wrap">
            <div class="catalog">
                <div class="catalog-item" auto-to="function1"><a>第1张</a></div>
                <div class="catalog-item" auto-to="function2"><a>第2张</a></div>
                <div class="catalog-item" auto-to="function3"><a>第3张</a></div>
            </div>
            <div class="content">
                <div menu="function1" class="section">
                    <h1>第一章</h1>
                </div>
                <div menu="function2" class="section">
                    <h1>第二章</h1>
                </div>
                <div menu="function3" class="section">
                    <h1>第三章</h1>
                </div>
            </div>
        </div>

    </div>

    <script type="text/javascript" src="jquery-2.1.4.js"></script>
    <script type="text/javascript">
        $(function(){
            Init();
        });
        function Init(){
            $(window).scroll(function() {
                var scrollTop = $(window).scrollTop();
                if(scrollTop > 50){
                    $('.catalog').addClass('fixed');
                }else{
                    $('.catalog').removeClass('fixed');
                }
                $('.content').children().each(function(){
                    var offSet = $(this).offset();
                    var offTop = offSet.top - scrollTop;
                    var height = $(this).height();

                    if(offTop<=0 && offTop> -height){
                        //去除其他
                        //添加自己
                        var docHeight = $(document).height();
                        var winHeight = $(window).height();

                        if(docHeight == winHeight+scrollTop)
                        {
                            $('.catalog').find('div:last-child').addClass('active').siblings().removeClass('active');
                        }else{
                            var target = $(this).attr('menu');
                            $('.catalog').find('div[auto-to="'+target+'"]').addClass('active').siblings().removeClass('active');
                        }


                    }
                });

            });


        }

    </script>
</body>
</html>